In October, Shurat HaDin filed a complaint with the National Labor Relations Board, the statutory body that enforces US trade union laws, to try to force UE to abandon its decision.

The complaint alleged that UE’s resolution violated the prohibition in US labor law against secondary boycotts.

Shurat HaDin is an Israeli organization that acts as a proxy for Israel’s Mossad spying and assassination agency. It uses legal cases to harass supporters of Palestinian rights, a strategy known as lawfare.

In a 12 January dismissal letter, the labor board said it had investigated the complaint against UE and found “there is insufficient evidence to establish a violation” of the law.

UE had told the board that Shurat HaDin’s action “was an attempt to interfere with the First Amendment rights of the union and its members to express opinions on political and international issues, and also that the Israeli firm’s allegation were factually untrue.”

Peter Knowlton, president of the 30,000-member UE, said in a statement that his union had in the past “withstood attempts by the US government to silence us during the McCarthy era in the 1950s,” and was “unbowed by the latest attempt of a surrogate of the Israeli government to stifle our call for justice for Palestinian and Israeli workers.”

Knowlton called the board’s decision “a victory for the growing BDS movement across the US, which faces increasing political attempts to silence and intimidate critics of the Israeli government.”

UE’s statement also revealed that Shurat HaDin’s attack on the union began with a 2 September 2015 letter to the General Electric Company, the largest employer of UE members, “warning” GE to “rescind its recently concluded labor agreement” with UE because of the resolution backing Palestinian rights.